Field of the Invention
The present invention relates to a power transmission device, particularly to a power transmission device for transmitting power from an engine to a transmission. Further, the present invention relates to a lock-up device, particularly to a lock-up device that is disposed between a torque converter body and a front cover coupled to an engine-side member to directly transmit power from the front cover to a turbine of the torque converter body.
Background Information
A torque converter is provided with a lock-up device to reduce fuel consumption. The lock-up device is disposed between a front cover and a turbine, and is configured to mechanically couple the front cover and the turbine to directly transmit torque therebetween.
The lock-up device includes a piston and a damper device as described in, for instance, Japan Laid-open Patent Application Publication No. JP-A-2009-293671. A friction member is fixed to the piston. The piston is configured to be moved by the action of hydraulic pressure, and accordingly, the friction member is configured to be pressed onto the front cover. Thus, torque is transmitted from the front cover to the piston. The damper device includes a plurality of outer peripheral side torsion springs, a plurality of inner peripheral side torsion springs and an intermediate member for coupling the outer peripheral side torsion springs and the inner peripheral side torsion springs. Further, the piston and an output-side member coupled to the turbine are elastically coupled by the torsion springs.
Moreover, as described in U.S. Pat. No. 8,135,525, there has been also provided a lock-up device intended to inhibit variation in speed of rotation to be transmitted to the output side by mounting an inertia member to the intermediate member for coupling the outer peripheral side torsion springs and the inner peripheral side torsion springs.
The lock-up device of U.S. Pat. No. 8,135,525 has the construction that the inertia member of the turbine and the elastic members are coupled to the intermediate member, and thus can inhibit variation in speed of rotation to be transmitted from the engine to the transmission in comparison with the device of the Publication No. JP-A-2009-293671.
However, the device of U.S. Pat. No. 8,135,525 has a drawback that the inertia member of the turbine resonates with variation in rotation speed of the engine, and this causes large variation in speed of rotation to be transmitted to the transmission when the rotation speed of the engine is low.